The present invention relates to a system, method and apparatus for enhanced steering for use in a watercraft, amphibian or other such vehicle, and in particular, but not exclusively, where the marine propulsion is provided by means of a jet drive.
Jet drive marine propulsion systems are well known in the art and typically comprise a prime mover and jet drive combination. The prime mover provides drive via a drive shaft which rotates an impeller arranged in a duct (conduit) of the jet drive. The duct comprises, at a first proximal end, an inlet generally arranged in the bottom surface of a hull of the watercraft or amphibian for inducting water upstream of the impeller, and, at a second distal end, an outlet generally arranged as an outlet nozzle downstream of the impellor for ejecting water as a jet. The nozzle is generally of a lesser cross-sectional area when compared to that of the duct so as to provide for pressurised and accelerated flow of the water through the duct under the action of the rotating impellor. Propulsion is thus provided by way of a reaction force to the thrust provided by the jet of water ejected via the outlet nozzle. Unlike in watercraft where a submerged rudder is used to effect steering, with a jet drive it is conventional to provide a steering nozzle downstream (to the rear) of the outlet nozzle, and in close registration thereto, which steering nozzle is pivotable about a generally vertical axis so that it may pivot left or right under the control of the steering and direct the jet of water exiting from the outlet nozzle accordingly. Thus, steering of the watercraft or amphibian is effected as a result of the reactionary force to the thrust of the jet exiting the steering nozzle, as steered.
The thrust and steering generated by the jet drive to power and steer the watercraft or amphibian is controlled by the driver or rider by way of a manually operated throttle control device (morse throttle, twist grip biased to idle, pivotable lever biased to idle, or other suitable device) and use of a steering device (wheel, handlebar, tiller, or other suitable device). A known limitation, therefore, with jet drive marine propulsion systems is a reduced (or total lack of) steering function when the manually operated throttle is set to low or idle, or let go and biased towards idle, regardless of a steering request via the steering device, because there is low or no thrust generated by the jet drive. This can present drivers or riders of the watercraft or amphibians with a situation of reduced manoeuvrability and control of the watercraft or amphibian unless the manually operated throttle control is re-applied by the driver or rider. In particular, this can be a problem when travelling at speed and the manually operated throttle is let go of and returns to idle. Typically, it is then no longer possible to steer the watercraft or amphibian effectively as the thrust generated by the jet drive falls away with reduced engine speed. Such a phenomenon is known as off-throttle or off-power steering loss. A number of prior art devices and systems have been developed in particular to deal with the phenomenon of off-throttle or off-power steering loss. Furthermore, at low speed, when attempting docking or beaching manoeuvres, a lack of meaningful steerable thrust has also been perceived by some drivers or riders as a problem, and so a number of prior art devices and systems have been developed to provide assistance with steerable thrust for low speed manoeuvres, such as docking and/or beaching. However, other drivers and riders have found steerable thrust assistance at low (and/or high) speed a positive hindrance as it provides steerable thrust when not intuitively expected and/or when not desired.
In the various prior art devices and systems proposed for addressing the phenomenon of off-throttle or off-power steering loss, a rapid off-throttle event and a threshold steering input is sensed, and often the speed of the watercraft is taken into consideration also. Based on these inputs, the prior art devices and systems either effect a re-application of throttle independently of the driver's or rider's use of the manual throttle control so that the jet drive generates steerable thrust, or a control system activates an elongated deceleration profile independently of the driver's or rider's use/non-use of the manual throttle control so as to slow the usual rate of throttle deceleration and thus slow the loss of steering thrust available via the jet drive.
A problem, therefore, with these known prior art devices and systems is that there is a lag between the device or system sensing a rapid off-throttle event (which is a necessary precursor and sensor input), and then subsequently determining the need for off-throttle or off-power steering. Typically, a threshold steering input is also required to be sensed before the device or system is turned on or implemented. What then follows is either a re-application of throttle, or a deceleration profile is turned on or implemented so as to slow the loss of steering thrust for a predetermined period of time. The resulting effect can provide for unusual and unsettling characteristics of the watercraft or amphibian, or the systems can provide unwanted thrust, particularly in the low speed docking/beaching assist systems. This has resulted in drivers and riders of the watercraft in question switching off entirely or removing the off-throttle or off-power steering and/or low speed docking/beaching assist devices and systems.